1. Field of the Invention
The present invention relates to a display device including plural pixel circuits.
2. Description of the Related Art
There are display devices including plural pixel circuits, each of which has a transistor, like liquid crystal display devices. For example, in display devices in which plural pixel circuits are arranged in a matrix shape, data signal lines are arranged to correspond to the columns of the pixel circuits and the pixel circuits are scanned in units of rows. A data signal indicating a gray level to be displayed by the pixel circuits to be scanned is input from the corresponding data signal line. The pixel circuits store the input data signal. A signal for selecting a row of the pixel circuits is output from a shift register circuit.
Here, the pixel circuits characteristics for storing the data signal may differ from each other due to a factor such as a difference in characteristic between the rows. Hereafter, a cause of the phenomenon in case of liquid crystal display device will be described. In the liquid crystal display device, the polarity of a voltage to be applied to liquid crystal is changed every predetermined time so as to prevent a ghost image. At this time, a method called N-line inversion may be used. In the method, the polarity of the data signal input to the data signal line changes whenever N rows are scanned. On the other hand, it is known that it takes a predetermined time for the potential of the pixel electrodes to vary to the potential of the data signal due to parasitic capacitance generated in the data signal lines and the like. The pixel electrodes apply a voltage to the liquid crystal. When the potential of the data signal greatly varies, it is difficult for the voltage applied to the liquid crystal to satisfactorily vary. In the N-line inversion, the variation in potential of the data signal when the polarity is changed is greater than the variation in potential of the data signal when the polarity is not changed. Thus there is a difference in the voltages applied to the liquid crystal between the row changed in polarity from the previous row and the row unchanged in polarity, thereby causing unevenness in brightness to be displayed.
JP2006-39542A discloses a display device that includes a dummy row in a shift register and that copes with the above-mentioned problem using an operation of scanning a dummy row. JP2002-287701A discloses a liquid crystal display device coping with the above-mentioned problem by changing the time of scanning rows by the use of a general shift register constructed in a driver IC.